Field of the Invention
The present invention relates to an automatic transmission for a vehicle. More particularly, the present invention relates to a planetary gear train of an automatic transmission for a vehicle capable of improving power delivery performance and fuel efficiency and securing linearity of an inter-stage part of shift stages by increasing a span of a gear ratio while implementing 9 forward speeds by as small a number of components as possible.
Description of Related Art
A recent rise in oil prices has caused unlimited competition toward improvement of fuel efficiency.
Therefore, research into a technology capable of decreasing weight and improving fuel efficiency through down-sizing of an engine has been conducted, and research into a technology capable of securing drivability and fuel efficiency competitiveness through multi-staging of an automatic transmission has been conducted.
However, as the number of shift stages in the automatic transmission is increased, the number of internal components is increased, such that mountability, cost, weight, transfer efficiency, and the like may be deteriorated.
Therefore, it may be important to develop a planetary gear train capable of generating maximum efficiency with a small number of components in order to increase a fuel efficiency improvement effect through the multi-staging.
In this aspect, recently, an 8-speed automatic transmission has been implemented, and research into and development of the planetary gear train capable of implementing shift stages of 8 speeds or more have been actively conducted.
However, recently, in the case of the 8-speed automatic transmission, since a span of a gear ratio is maintained in a range of 6.5 to 7.5, there is a problem that a fuel efficiency improvement effect is not large.
Therefore, in the case in which a span of a gear ratio of the 8-speed automatic transmission is 9.0 or more, linearity of an inter-stage ratio of shift stages may not be secured, such that operation efficiency of the engine and drivability of a vehicle are deteriorated. Therefore, the development of a high-efficiency automatic transmission of 9 speeds or more has been demanded.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.